Soybean rust: Coming to field near you?

Cecil H. Yancy Jr. | Aug 13, 2003

The devastating, airborne fungus has already cut a wide swath in soybean crops in Asia, Australia and Africa, and it’s on the move in the Western Hemisphere.

Since it was discovered in South America in 2001, soybean rust has moved from Paraguay to near the Equator in Brazil. In 2003, the disease cost Brazilian farmers $1.3 billion in lost yield and chemical application. While it’s on track to arrive in the United States in two to three years, one researcher points out that “one hurricane” could bring it sooner.

In a news conference at the annual meeting of the American Phytopathological Society in Charlotte, N.C., there was a sense of urgency in getting out the message of the potential damage that soybean rust could cause the U.S. soybean industry. USDA soybean researchers based in Zimbabwe and Brazil added perspective to the serious threat that soybean rust poses to the U.S. soybean industry.

USDA, the United Soybean Board and the American Soybean Association are leaving little to chance as they prepare for “when” soybean rust arrives on the air in the U.S. Checkoff funds have been used to develop diagnostic tools to help farmers and researchers identify the symptoms of the fungus.

A worldwide soybean breeding effort is looking for resistance, and chemical companies are reportedly looking at additional compounds for the control of soybean rust. Currently, two fungicides are registered for control of soybean rust in the U.S.

“It’s not a matter of if, it’s a matter of when soybean rust will hit the United States,” says Brian Hieser, a Minier, Ill., soybean farmer and chairman of the United Soybean Board’s production committee.

Premature defoliation

Soybean rust causes legions on plants that can lead to premature defoliation and decreased yields.

But it’s “extremely difficult to identify” and takes expert knowledge of the disease, says Clive Levy, a soybean researcher with a farmers’ cooperative in Zimbabwe. “The symptoms are just above the microscopic level and it takes a hand lens to identify. It starts at the bottom of the plant at flowering.” Soybean rust can also be confused with a number of diseases, including brown rust.

The United Soybean Board has a diagnostic guide available on its Web site at www.unitedsoybean.org. A printed copy can be ordered by calling 1-888-235-4332.

More information on soybean rust is also available at the USDA’s Animal Plant Health and Inspection Service’s Plant Protection and Pest Detection Quarantine Web site at www.aphis.usda.gov/ppq.

The American Phytopathological Society also has information on the disease under directories and rosters at www.apsnet.org.

Fast moving

“One factor that farmers will notice very early on is the stalks turn yellow and the plant looks sick,” Levy says. “When the disease first arrived in Zimbabwe (in 1998), it moved rapidly taking the plants over in five or six days.” Early on, the advice was to check for symptoms, then apply fungicide. Now the advice is, “treat in advance of symptoms.

“We’ve had quite large areas where 80 percent of the crop has been destroyed,” Levy says. When chemicals are applied on a timely basis, the losses have been in the 20-percent range in Zimbabwe. “Where farmers do have failures, it’s due to poor timing of applications. It explodes very rapidly on the plant and if applied too late, you won’t be able to control it.”

Jose Tadashi Yorinori, a USDA soybean rust researcher with the Brazilian Agricultural Research Cooperation, says soybean rust was found in 90 percent of soybean acres in Brazil this past season, having traveled some 3,500 kilometers in two years. He says most of the fungicide failures in the field were due to “farmers deciding to do something too late.”

Outside the U.S., growers have a wider array of chemicals to use for the control of soybean rust; however, of five materials screened for soybean rust in Brazil last year, only two performed well, Yoriniori says. “This is an important question that needs a lot of experimenting before a fungicide is released.”

In the United States, Quadris and chlorothalonil products such as Bravo are registered for control of soybean rust. Syngenta makes both chemicals. Section 18 efforts are underway in Minnesota and South Dakota to get emergency registrations for chemicals should soybean rust emerge in the United States, experts say.

The take-no-chances approach in the U.S. regarding the disease has been in progress for more than a year and mirrors the effort in South America. “We have a big, big problem here,” Yorinori says. “We were accused of terrorizing the farmers. We are not rooting for it to happen … we couldn’t respond fast enough.” To put the potential threat of soybean rust into perspective, consider that there would not be enough crop protection fungicides to control an epidemic of the disease on the nation’s 77 million acres of soybeans, says the USDA’s Monte Miles, a plant pathologist at the University of Illinois.

Awareness growing

Although it hasn’t arrived in the United States, awareness of soybean rust is generally high across the country, Hieser says. USDA-APHIS has a rapid response team to diagnose, confirm and recommend actions with a network of five diagnostic centers across the country.

APHIS doesn’t plan to quarantine fields with soybean rust, says Anwar Rizvi, the program manager for soybean rust with APHIS. Rizvi was in the audience at the press conference and answered questions. “The attitude from APHIS’ point of view is to develop a management strategy,” Rizvi says. “Soybean rust will spread from a natural source, which is a hurricane and wind. There will be a team of at least 20 people on notice in 24 hours or less” should an outbreak occur. Rizvi points out that when a case of soybean rust is confirmed, it likely means the disease is also in the adjacent area. In the event of an outbreak, the American Soybean Association and the United Soybean Board will be consulted.

The soybean industry met last year to decide the role each organization would take in regard to the threat of soybean rust. Speakers at the news conference agreed that research would play a huge role in the management strategy of soybean rust.

No resistant to soybean rust has been found in more than 900 commercial soybean varieties in the Midwest and South, says Monte Miles, an ARS plant pathologist at the University of Illinois.

A short list of soybean ascensions will be evaluated overseas, says Glen Hartman, a USDA soybean pathologist at the University of Illinois. In Asia, resistant varieties are being crossed with elite germplasm.

“One of our charges is research coordination,” Hieser says. “USB is able to move fairly quickly when something like this does develop. In the short term, the United Soybean Board has a good role in getting the basic research going.”

For example, in the first year of proposals, United Soybean Board didn’t have extensive field trials of fungicides, but now tests are being conducted in Zimbabwe.

Fungicides are the first line of defense. “We’ve made some progress,” says Reid Frederick, a research molecular biologist with the USDA’s Foreign Disease-Weed Science Research Unit in Fort Detrick, Md. “Chemical companies are aware of the problem.”

In the very, very long term, the second strategy is developing tolerant varieties. “That’s going to take time,” Frederick says.

Researchers across the globe are staying in contact with each other on a monthly basis through conference calls, says Rizvi of the Animal Plant Health and Inspection Service. Plans are now being made to hold a conference on soybean rust later this year, he says.